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The current Ebola epidemic in West Africa is the largest in history and is unprecedented in many ways, including the large number of healthcare workers who have been infected while treating patients. The large scale of the epidemic, as well as the two healthcare workers who contracted Ebola while caring for the first case in the United States, has directed particular attention to the personal protective equipment (PPE) used by healthcare workers to reduce their risk of infection. PPE is designed to create a barrier to prevent pathogens from entering the body through the mucous membranes or broken skin. Examples of PPE used for Ebola include (but are not limited to) gloves, gown/coverall, mask/respirator, apron, faceshield/goggles, and cap/hood (see Figure 1). Reports from healthcare workers in West Africa indicate that some personnel are able to wear their PPE for only 40 minutes at a time because of the high ambient temperature and humid conditions. Even in the United States, where management of patients with Ebola is done in air-conditioned environments, uncomfortable PPE is a common complaint and causes additional burden for healthcare workers.

On September 26, 2014, in a speech at the Global Health Security Agenda Summit, President Obama announced a “Grand Challenge” to design improved PPE for use by healthcare workers during treatment of Ebola patients.

“And today, I’m pleased to announce a new effort to help health workers respond to diseases like Ebola. As many of you know firsthand, the protective gear that health workers wear can get incredibly hot, especially in humid environments. So today, we’re issuing a challenge to inventors and entrepreneurs and businesses of the world to design better protective solutions for our health workers. If you design them, we will make them. We will pay for them. And our goal is to get them to the field in a matter of months to help the people working in West Africa right now. I’m confident we can do this.”

The National Institute for Occupational Safety and Health (NIOSH), along with other offices in the U.S. Centers for Disease Control and Prevention (CDC), is partnering with the U.S. Agency for International Development (USAID), the White House Office of Science and Technology Policy (OSTP), the U.S. Department of Defense (DOD), and other U.S. agencies on the Fighting Ebola: A Grand Challenge for Development (Grand Challenge) to help healthcare workers on the front lines provide better care and stop the spread of Ebola. The USAID-led Grand Challenge consists of several initiatives, including developing, testing, and scaling entirely new PPE or modifications to current PPE that address issues of protection, heat stress, and comfort for healthcare workers. Key components of the Grand Challenge include broadly soliciting new ideas through social media (crowdsourcing), forging public/private partnerships, and providing critical funding for promising designs.

How NIOSH is Supporting the Grand Challenge and PPE Needs for the Ebola Response

For the past five months, NIOSH has evaluated the PPE ensembles currently used in West Africa and around the world (see Figure 1) for Ebola and collaborated nationally and internationally on efforts to develop solutions to improve PPE configurations in the future. NIOSH prioritized internal efforts to help inform healthcare workers and infection control and safety professionals about PPE best practices and selection options, including managing heat stress, identifying strategies for selecting protective clothing, and identifying NIOSH-approved powered-air purifying respirators consistent with CDC recommendations for use in managing patients with Ebola.

NIOSH is working closely with USAID, OSTP, and other federal partners on the Grand Challenge, including (but not limited to) participating in crowdsourcing events to promote innovation, reviewing promising ideas that can be scaled to the field, and setting performance, test, and evaluation requirements. NIOSH conducts research that supports the epidemic response and the Grand Challenge. A previous NIOSH science blog identified eight knowledge generation priorities for protecting workers from Ebola. Examples of current efforts include the following:

NIOSH is using its sweating thermal manikin and conducting tests involving human subjects to evaluate several common PPE ensembles used in West Africa and around the world (see Figure 1) to better understand factors associated with heat stress and design features that affect comfort and job performance. The evaluation findings will be used to refine PPE recommendations. Data on the impact of wearing specific combinations of PPE are nonexistent (for example, how does putting an apron on top of a surgical gown affect heat stress?). Preliminary findings (unpublished) support anecdotal reports from healthcare workers in West Africa that certain PPE combinations will be difficult to wear for longer than 40 minutes in high heat and humidity conditions. These evaluations are critical because they set the baseline for the Grand Challenge. PPE manufacturers are constantly improving barrier materials and NIOSH plans to test innovative PPE prototypes as well as cooling systems proposed in response to the Grand Challenge as part of this evaluation effort. Overall, data from these tests are expected to help inform PPE selection options that allow healthcare workers to wear PPE for longer periods of time without undue stress or burden.

NIOSH is performing research on isolation gowns (a common component of some PPE ensembles used in the Ebola epidemic) to evaluate their durability and ability to prevent penetration of viruses in blood and body fluids through the material. The findings of this project will be used in the development of a new standard specification for isolation gowns. This study builds upon NIOSH’s previous experience working with standards development organizations to establish PPE standards for prehospital workers (for example, emergency medical services workers and other medical first responders). The study will also help set the baseline for the Grand Challenge by providing performance data (e.g., tensile strength, tear strength, seam strength, water resistance, viral penetration, air permeability, etc.).

NIOSH is undertaking studies to better understand key factors affecting penetration of microorganisms in blood and body fluids through protective clothing, such as the surface tension of the carrier liquid and microorganism size and shape. In one set of experiments, the “elbow lean test” is used to quickly evaluate different types of aprons, gowns, and coveralls under simulated use conditions with varying liquids of different surface tensions. In other experiments, NIOSH researchers use a modified version of the ASTM F1671 test method to study penetration of surrogate viruses of different sizes and shapes. These experiments will be used to advance protective clothing standards, validate or improve upon existing test methods, and inform the PPE selection process for protection against infectious pathogens like Ebola that spread via contact with blood and body fluids.

What Is Currently Known about Balancing Protection and Comfort?

Many workplace settings (construction, agriculture, wildland firefighting, hazardous materials response, manufacturing) require employees to wear PPE for extended periods of time in hot, humid, and extremely challenging environments. PPE reduces the ability of the wearer to cool off by limiting heat transfer from the body through sweat evaporation, convection, and radiation. PPE also adds to the amount of weight carried, further increasing heat load. However, the challenges faced in selecting PPE for the current Ebola epidemic in West Africa are unique. The selection of work-rest cycles to mitigate heat stress are constrained by the lack of single-use PPE, the extreme patient load (more and/or longer rest breaks are not practical), and limited staff to treat critically ill patients with Ebola.

Selecting PPE requires balancing protection and comfort/heat stress. This is not a new issue, nor is it unique to the Ebola epidemic. In general, discomfort increases with increased protection. To provide protection, PPE designers often must make certain sacrifices; sometimes, these include material choices (for example, using materials that are known to block blood and body fluids containing infectious materials from breaking through) that make the PPE less breathable and, thus, less comfortable for the wearer because it increases heat stress. Reducing protection is usually not a viable option, so the focus is on managing heat stress. The industrial hygiene community has decades of experience in developing strategies (for example, work-rest cycles) to manage heat stress, including “clothing adjustment factors” to account for the extra burden of the PPE

Another important aspect of the protection versus comfort trade-off is addressing the question, “What PPE constitutes an ’acceptable’ level of protection against pathogens like Ebola virus in blood and body fluids?” Fortunately, requirements and methods to evaluate the performance of PPE have been written by organizations that develop voluntary consensus standards. The most common standard in the United States for classifying healthcare protective apparel, including surgical and isolation gowns, is ANSI/AAMI:PB70 (2012). This standard defines four levels of liquid barrier performance, with Level 1 being the lowest level of protection and Level 4 being the highest level of protection. In addition to the highest level of liquid barrier performance, AAMI Level 4 gowns are tested for penetration of viruses using the ASTM F1671 test method. Barrier materials passing this test are considered impervious to viruses under normal use conditions. In other words, only PPE passing this test or similar tests done in Europe (ISO 16604) have been demonstrated to block viruses in simulated blood and body fluids from passing at a certain level of pressure (for example, to simulate leaning on a contaminated object) through the materials. See The National Personal Protective Technology Laboratory (NPPTL) website for a more detailed summary of the key protective clothing standards and test methods used in healthcare to assess protection against microorganisms in blood and body fluids.

To highlight the challenges in balancing comfort and protection, we created a table that summarizes what is currently known about the types of PPE commonly used in the Ebola epidemic. PPE are listed in order of expected levels of protection against pathogens in blood and body fluids, starting with the least protective PPE with the least amount of body coverage. For detailed PPE selection guidance for Ebola patient management, see CDC, the Occupational Safety and Health Administration, and the World Health Organization.

NIOSH hopes that the information in this blog will continue the dialogue on solutions to permit healthcare workers to wear their PPE safely and with less stress and burden for longer periods of time during patient care.

Ronald Shaffer, PhD

Dr. Shaffer is Chief of Technology Research Branch at NIOSH’s National Personal Protective Technology Laboratory.

For more information about Ebola, heat stress, or the NIOSH personal protective technology (PPT) program, visit the following websites:

Limited to front torso, upper legs, and arms. May have noncontinuous coverage in back.

Low

Chemical Protective Apron

n/a

Fluid/chemical resistant and generally pass viral penetration tests.

Limited to front torso and upper legs.

Medium

Limited use Chemical Protective Coverall3

n/a

Fluid/chemical resistant and generally pass viral penetration tests.

Full-body coverage except feet, hands, and face.

Medium – High

Details of which standards specific products have been tested against are often found in the PPE user instructions or available on the PPE manufacturer’s website.

Based upon measured and estimated clothing adjustment factors in units of wet bulb globe temperature, with low defined as <2° C, medium ranging from 2-4° C, and high being greater >4° C. Clothing adjustment factors based upon data from the literature for aprons and coveralls and expert opinion of NIOSH researchers for gowns. Ranges reflect differences among manufacturers and across the different models within that type and may not include all of the PPE worn by healthcare workers during an Ebola epidemic.

Includes microporous or selectively permeable membranes such as multi-/single-layer nonwoven fabrics.

27 comments on “Fighting Ebola: A Grand Challenge for Development – How NIOSH is Helping Design Improved Personal Protective Equipment for Healthcare Workers”

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I have been advocating for a number of years in specifying components (elements) for “workplace space suits” as for example Hazmat Workers, Firefighters, High Voltage Electrical Workers and NASA specialists may be required to use them (e.g. in fueling the rockets). About the NASA’s Propellant Handlers Ensemble (PHE) please contact Michael Cardinale, CIH _and_ John C. Ratliff, CSP, CIH, MSPH .

With the evolution of microfiber garments, I question if such “underwear” could be used to remove the sweat from the skin surfaces. As long as workers remain hydrated and their sweat is continually removed, the workers wearing them should be safe from heat illness and feel comfortable. Could we use a form of electrolysis to remove (i.e. “move alone”) the sweat absorbed in the microfiber garments?

It is my personal understanding that the Late Francis Duke-Dobos, MD was working on apparel ensembles with an ASTM Committee, while Professor Emeritus at the University of South Florida in Tampa, Florida. The experimental work inside their “heat stress laboratory” (i.e. a specialized sauna) may be now managed by Professor Thomas E. Bernard .

Lastly we could use PAPR helmets to cool the worker’s head and provide the necessary respiratory protection from airborne bodily aerosols (the “droplets” and all). This may sound like science fiction but could be a plausible PPE design.

1. The idea of using wicking undergarments to aid in cooling and comfort is certainly appealing, although its benefit while being worn underneath PPE has shown little effect on human subject heart rate, core temperature, rating of perceived exertion, thermal discomfort, and thermal strain in a previous study involving firefighter PPE [Smith et al., 2014]. One of the USAID-funded Ebola Grand Challenge winners (http://www.ebolagrandchallenge.net/safer-and-faster-ppe) is planning to explore this concept for Ebola PPE.
2. ASTM’s F23 committee on Personal Protective Clothing and Equipment develops standard specifications, test methods, practices, guides, terminology, and classifications for protective clothing and personal protective equipment (PPE) designed and constructed to protect the user from potential occupational hazards and/or provide a barrier to prevent the user from being a source of contamination. NIOSH contributes to ASTM’s 23.6 human factors subcommittee, including leading the development of standards related to physiological and ergonomic testing of PPE ensembles such as F2668-07 (http://www.astm.org/Standards/F2668.htm) and work item 27291 (http://www.astm.org/DATABASE.CART/WORKITEMS/WK27291.htm)
3. As discussed in our response to John Ratliff, air crossing the face from a PAPR gives a sensation of coolness and decreases facial temperatures, but available data suggests that there is little to no impact on core body temperature.

I see no mention of respiratory protection in the above blog. CDC at first was recommending surgical masks, and then upgraded this to N95 respirators or PAPR (powered air-purifying respirators) for use with Ebola patients. This was after an AIHA on-line discussion on PPE for Ebola, which I participated in. It appears that Ebola can be transmitted by airborne aerosols, although that is not a primary means of transmission (contact with liquids from an infected patient is primary). Because of this, industrial hygienists are recommending an air purifying respirator, and some IHs are saying that even an N95 respirator may not be adequate because they allow a limited amount of aerosols through the respirator (95% effective). They say that because they cannot recommend an N95 respirator for asbestos, they cannot recommend an N95 respirator for Ebola. My thoughts are that the PAPR respirator should be used, as it has better filtering properties, and also decreases the heat stress by providing cooling air over the head of the person. I have experience in the chemical blending industry with workers using a PAPR with Level B and Level C chemical-resistant clothing, and they really like it. I’m curious whether the NOISH sweating thermal manikin has been tested with higher level protection (such as the Limited-Use Chemical Coverall) and the PAPR, and if there is data on the thermal effects of the PAPR itself? If so, maybe that could be added to this blog. If not, can these tests be conducted and then published here? Thank you for the blog, as it will be very helpful to people.

Thanks for commenting on the blog! Your comment included multiple topics and we’ll address each one separately.

1. You are correct we did not specifically address respiratory protection in the blog, although you will note that the picture in Figure 1 includes an N95 filtering facepiece respirator (FFR). The PPE ensemble configurations we used for the sweating thermal manikin and human testing discussed in the blog were based upon what is commonly used internationally. Some of these configurations include N95 FFRs. For hospitals in the United States, CDC put together a nice video explaining the rationale for recommending respiratory protection during management of Ebola patients here: https://www.youtube.com/watch?v=8y19h1hecgY&feature=youtu.be

2. Ebola is not transmitted by an airborne route. In the United States, respiratory protection is recommended to protect healthcare workers in case there is a planned or unplanned need for an aerosol-generating procedure. Either N95 FFRs or PAPRs will provide protection from Ebola transmission during aerosol-generating procedures and both have been used safely to care for patients with Ebola in the US. Local decisions on whether to use N95 FFRs or PAPRs are based upon a number of factors, including:

• N95 FFRs are disposable, while PAPRs need to be disinfected after each use.
• N95 FFR can be easier to put on and remove for those who are not familiar with PAPRs.
• Some people might find PAPRs are more comfortable because of the air circulation in the hood.
• N95 FFRs are easier to store and create less medical waste when disposed.
• Tight-fitting respirators cannot be used by people with facial hair if it interferes with the face seal.
• If using N95 FFRs, all healthcare workers must be fit tested to ensure a proper fit and tight seal, and to ensure that facial hair would not interfere with the safe use of an N95 FFR. PAPRs can be worn by those with facial hair.

3. In general, protective facemasks, including different types of respirators have minimal impact on core body temperature (Roberge, 2012). This is because only 10-15% (depending on work rate) of body heat is released via the respiratory tract. The sensation of increased body heat is from three potential sources: 1) the area of the face that is covered by a surgical mask or N95 FFR is very thermosensitive because it has a higher number of sensory nerve endings (e.g., lips, perioral area) than other areas of the face and increased afferent impulses (via the Trigeminal Nerve) are directed to the brain, 2) breathing warmed air has been shown to result in increased thoracic temperature, and 3) breathing in warm air may result in brain warming. The air crossing the face from a PAPR gives a sensation of coolness and decreases facial temperatures (Caretti et al, 2014), but would have little to no impact on core temperature. From current reports (Wolz 2014) and through conversations with field deployers, some healthcare workers treating Ebola patients in West Africa can tolerate wearing commonly available PPE ensembles (TyChem coveralls, Tyvek hood, rubber apron, rubber boots, gloves, goggles, etc.) for as little as 40 minutes. This is unlikely to change whether using a surgical mask, disposable N95 FFR, or a PAPR. Work time is more likely to be driven by the wearing of a full body PPE (and thus driving up core body temperature), than by the type of facial protection (which affects subjective comfort). For example, work done by the US Army (Caretti, 2002) found that the protective suit may be the greatest contributor to physiological thermal load during heat exposure. Lastly, work from Fletcher et al (2014) evaluated the contribution to heat stress from a full facepiece respirator (“worst case” scenario) during exercise while wearing different combinations of PPE. They found differences in physiological responses among the PPE ensembles tested, but the respirator was not a contributor to the heat stress.

4. We have not done any experiments to date with a PAPR on the sweating thermal manikin. Thank you for the suggestion. We have tested a number of different types of protective ensembles with the manikin. For example, one of our recent published studies [Kim et al, 2014] evaluated the thermal characteristics of two PPE ensembles comparing the various test methods, including the sweating hot plate, sweating thermal manikin, and human tests.

I feel another very key component to the Ebola PPE discussions are the environmental controls that we have here in the US versus what is available in Africa. I’m not sure that the same type of PPE needed in Africa is needed in the US; in addition, stage of disease is another important factor in PPE selection decisions. Thanks for the info and I, too, would appreciate seeing updates in this blog.

Very good comments. We agree that the PPE needs for workers in West Africa can sometimes be different from that for workers in the United States. NIOSH is conducting research to assist organizations in understanding how PPE should be selected and used by workers, domestically and internationally, during care of Ebola patients. Stage of the disease is another important factor. For example, CDC has developed an algorithm for domestic hospital emergency department’s to evaluate and manage patients with possible Ebola virus disease (http://www.cdc.gov/vhf/ebola/pdf/ed-algorithm-management-patients-possible-ebola.pdf). That algorithm has different PPE options based upon the based on the patient’s clinical status.

Concerning the role of respiration in heating or cooling, I’m not sure I believe the reference to these studies. That was my initial reaction, but now thinking about it I have some more thoughts. Any negative pressure respirator will place somewhat of a demand on the wearer, and this can build up a bit of heat. But these respirators do not subtract or add any heat from the ambient air, and this is important to this discussion.

One of the reasons is that I have heard from divers using rebreathers that they stay warm longer than on open circuit scuba because the rebreathers send the breath through a CO2 scrubber, which heats the air somewhat. So at least for divers diving deep and long, apparently respiration has an effect on cooling rates.

Concerning heating, I seem to remember that part of the treatment for immersion hypothermia is to not only apply external heat to the groin, sides of the chest and neck (carotid arteries), but also to administer heated oxygen to heat the body’s core.

…Beside this strategic donation of heat, inhalation rewarming also eliminates respiratory heat loss, which accounts for 10% to 30% of the body’s heat loss. This is particularly important in rescue situations where the ambient air is cold (cooling of the core through respiration). This cooling, if not stopped, can lead to ventricular fibrillation. Thermally stabilizing a patient, with suitable equipment, is necessary…http://www.hypothermia.org/hypothermia3.htm

Wouldn’t the converse also be true, that hot environmental air could account for 10-30% of heating? Perhaps the respirator itself has no influence on the temperature of the air being breathed. In this case, perhaps refrigerating the air from a PAPR could help.

For these reasons, I’m curious what the results will be for the NIOSH sweating manikan when tested with PAPRs in a hot environment?

I think there may be an application of cooling the air in a PAPR for those in more tropical climates, thereby keeping the health care workers cooler. That could fairly easily be done with ice packs around the large air hose to the hood. As stated above, I have experience with workers in the chemical blending industry, wearing full Level C chemical protective equipment and PAPR respirators. They felt that in this environment, they were more comfortable, perhaps because they were wearing hoods and the air was streaming over their heads, causing evaporative heat loss. I am retired, but still have contacts there. Would it help to ask them to experiment with cooling the air with ice packs on the large air hose?

Your suggestion to cool the air within the PAPR is interesting. We are not aware of any attempts to combine head skin cooling or cooling the air inside the PAPR. However, the basic concept of cooling the head/face or breathing in cool air to reduce core body temperature has been studied, but with mixed results (see references cited below). For example, one study (Desruelle and Candas, 2000) found that face skin cooling caused a slight reduction in heat strain, while cool air breathing had no effect. In general, there is minimal effect on cooling of core temperatures with the inhalation of cold air (Hartung et al, 1980). This is likely due to the fact that the respiratory tract plays only a minor role in temperature control.

Desruelle, A. V., and V. Candas. “Thermoregulatory effects of three different types of head cooling in humans during a mild hyperthermia.” European journal of applied physiology 81.1-2 (2000): 33-39.

(1) Would you have anybody at NIOSH who could comment on the idea of keeping the skin relatively dry by using the micro-fiber garments under or as part of tight-filling whole-body PPE?

(2) Concerning: “In the United States, respiratory protection is recommended to protect healthcare workers in case there is a planned or unplanned need for an aerosol-generating procedure. Either N95 FFRs or PAPRs will provide protection from Ebola transmission during aerosol-generating procedures and both have been used safely to care for patients with Ebola in the US.” African patients with Ebola do not sneeze or cough?1 With a high case mortality rates (up 100%) I would want a “Space Suit”!

Thank you for your comments. In regards to your comment on using wicking microfiber undergarments to keep the skin try, this is certainly appealing and is the subject of on-going research and development. In regards to your comment of requiring “space suit” protection, the CDC has put together a very useful webpage and a frequently asked questions list on the modes of Ebola transmission: http://www.cdc.gov/vhf/ebola/transmission/. I would refer you to this page and the “related links” section on that page.

According to the Frequently Asked Questions page, http://www.cdc.gov/vhf/ebola/transmission/qas.html, “There is no evidence indicating that Ebola virus is spread by coughing or sneezing. Ebola virus is transmitted through direct contact with the blood or body fluids of a person who is sick with Ebola; the virus is not transmitted through the air (like measles virus). However, droplets (e.g., splashes or sprays) of respiratory or other secretions from a person who is sick with Ebola could be infectious, and therefore certain precautions (called standard, contact, and droplet precautions) are recommended for use in healthcare settings to prevent the transmission of Ebola virus from patients sick with Ebola to healthcare personnel and other patients or family members.”

Finally, thank you for bringing these articles to our attention. Readers of the NIOSH science blog may find these interesting and helpful.

It creates the impression that Ebola can be transmitted via airborne vaporizers, in spite of the fact that that is not an essential method for transmission (contact with fluids from a tainted patient is essential). As a result of this, modern hygienists are suggesting an air cleansing respirator, and a few IHs are stating that even a N95 respirator may not be sufficient in light of the fact that they permit a constrained measure of pressurized canned products through the respirator (95% compelling). They say that in light of the fact that they can’t prescribe a N95 respirator for asbestos, they can’t suggest a N95 respirator for Ebola.

You are correct; Ebola is not transmitted normally by an airborne route. However, in the United States, respiratory protection is recommended to protect healthcare workers in case there is a planned or unplanned need for an aerosol-generating procedure (AGP) such as an intubation, suctioning, or active resuscitation. There are several pathogens, including viral hemorrhagic fevers, in which respirators are recommended during AGPs (see for example Appendix A in CDC and HICPAC’s 2007 Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings: http://www.cdc.gov/hicpac/pdf/isolation/Isolation2007.pdf).

The role of AGPs in disease transmission is the subject of on-going research. Recent studies (Tran et al, 2012; Macintyre et al 2014; Pshenichnaya and Nenadskaya, 2015) have found that some medical procedures are potentially capable of generating infectious aerosols and have been associated with increased risk of transmission to healthcare workers.

According to the OSHA respiratory protection standard all NIOSH certified half-mask air purifying respirators have an Assigned Protection Factor (APF) of 10, regardless of filter type (e.g., N95 or N100). https://www.osha.gov/Publications/3352-APF-respirators.pdf The Assigned Protection Factor of 10, equivalent to your Total Inward Leakage (TIL) of up to 10%, is attributed mainly to the leakage at the mask-face interface, i.e. the fit of a half-mask respirator.

A Fast Track Article published in the recent issue of the Journal of Occupational and Environmental Medicine (JOEM) titled: “Aerosol Transmission of Infectious Disease” by Rachael M. Jones, PhD and Lisa M. Brosseau, ScD in summary states that:

Objective: The concept of aerosol transmission is developed to resolve limitations
in conventional definitions of airborne and droplet transmission.
Methods: The method was literature review. Results: An infectious aerosol
is a collection of pathogen-laden particles in air. Aerosol particles may deposit
onto or be inhaled by a susceptible person. Aerosol transmission is
biologically plausible when infectious aerosols are generated by or from an
infectious person, the pathogen remains viable in the environment for some
period of time, and the target tissues in which the pathogen initiates infection
are accessible to the aerosol. Biological plausibility of aerosol transmission
is evaluated for Severe Acute Respiratory Syndrome coronavirus
and norovirus, and discussed for Mycobacterium tuberculosis, influenza, and
Ebola virus. Conclusions: Aerosol transmission reflects a modern understanding
of aerosol science and allows physically appropriate explanation
and intervention selection for infectious diseases.

In the article you referenced, Professors Jones and Brosseau review available literature on aerosol transmission of infectious diseases, including Severe Acute Respiratory Syndrome coronavirus, norovirus, Mycobacterium tuberculosis, influenza, and Ebola virus. Their paper includes an alternative classification scheme, proposed by the authors, for assigning whether a particular pathogen should be considered a low or high concern for aerosol transmission.

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